Ink jet printing is a non-impact printing method that produces droplets of ink that are deposited on a substrate such as paper or transparent film in response to an electronic digital signal. Thermal or bubble jet drop-on-demand ink jet printers have found broad application as output devices for personal computers in the office and the home.
A great concern with ink jet printing, especially on "plain paper," is print quality. The term "plain paper," as it is commonly understood, means a broad set of commercial papers, especially those available for use in electrographic copying, that do not rely on a unique structure, composition, or narrow set of properties such that the ink jet printer can only use this one specific type of paper. In recent years, there has been an increasing demand in the marketplace for plain paper printing devices.
Print quality can be defined as the image definition or contrast verses the nonimage background areas. It is controlled by 2 general factors:
1) Color properties of the ink which are measured by optical density and color coordinates controlling hue, e.g., L*, A* and B* in the CIELAB 1976 color standards. In the case of black inks the optical density is the most important of these two factors.
2) Non-color image characteristics which determine the definition of the image are:
a) resolution, i.e., number of drops of ink per unit area; PA1 b) the area coverage per drop; PA1 c) edge acuity or sharpness; and PA1 d) extent of presence of artifacts such as satellite droplets, side pennants or feathering. PA1 (a) an aqueous carrier medium; PA1 (b) a colorant selected from the group consisting of a pigment dispersion and a dye; and PA1 (c) a cosolvent having a solubility in water of at least 4.5% at 25.degree. C., and which is selected from the group of: PA1 R=--H or an alkyl group of 1-4 carbons; PA1 R'=--H, an alkyl group of 1-3 carbons, or an alkyl group of 1-4 carbons containing one hydroxyl group; PA1 X=--H or --CH.sub.3 independently; PA1 n=1-200; PA1 R"=an alkyl group of 1-4 carbons; and PA1 Y is a divalent connecting group of atoms selected from the group consisting of: ##STR1## PA1 R, R', X, and Y are as defined above; and PA1 n=2-400; PA1 n+p+q=3-500; and PA1 a=0 or 1; PA1 R, R', and X are as defined above; PA1 n=1-200; PA1 R"=an alkyl group of 1-3 carbons; and PA1 Y is a divalent connecting group of atoms selected from the group of: ##STR3## PA1 Type (1) is prepared from a monoamine and a monofunctional derivatizing reactant; PA1 Type (2) is prepared from a diamine and 2 moles of a monofunctional derivatizing reactant; PA1 Type (3) is prepared from a triamine and 3 moles of a monofuctional derivatizing reactant; and PA1 Type (4) is prepared from a 2 moles of a monoamine and one mole of a difunctional derivatizing reactant.
The ink jet inks of this invention produce high optical densities and give images of high definition free of artifacts such as feathering. In addition, the inks of this invention impart this excellent print quality in both dye and pigment-based inks and, with respect to the latter, without deleterious effects on pigment dispersion stability. The inks of this invention also impart freedom from film formation on the nozzle resistors in pigmented inks and do not adversely affect other ink properties such as decap time or crusting.
These results are surprising and unexpected because the polyoxyalkyleneamines themselves are poor cosolvents for aqueous ink jet inks. They produce low optical densities, cause flocculation of pigment dispersions and induce blockage of pen nozzles.